Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N30: Strongly Correlated Systems, Including Quantum Fluids and Solids XII |
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Sponsoring Units: DCMP Chair: Brenden Ortiz, University of California, Santa Barbara Room: Room 222/223 |
Wednesday, March 8, 2023 11:30AM - 11:42AM |
N30.00001: Magnetic field and frustration induced quantum spin liquid in a J1-J3 honeycomb XY model Anjishnu Bose, Sreekar Voleti, Arun Paramekanti
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Wednesday, March 8, 2023 11:42AM - 11:54AM |
N30.00002: Gapped and gapless topological order in interacting Weyl semimetals Anton Burkov, Xuzhe Ying, Lei Gioia, Chong Wang It has recently been demonstrated that it is possible to open a gap in a magnetic Weyl semimetal, while preserving the chiral anomaly along with |
Wednesday, March 8, 2023 11:54AM - 12:06PM |
N30.00003: Parafermion zero modes and fractional Josephson tunneling in fractional quantum Hall-superconductor hybrid structures Junyi Cao, Eduardo H Fradkin We consider a hybrid structure of two narrow fractional topological superconductors, consisting of a Laughlin ν=1/m fractional quantum Hall state with two narrow s-wave superconductors. The edge states of the Laughlin state become superconducting by the proximity effect. The effective field theory for such system consists of two sine-Gordon theories coupled by parafermion tunneling. We identify the parafermion zero modes at the ends of fractional topological superconductors as "half" of a quasiparticle pair. We compute the parafermion tunneling current and show that it exhibits an anomalous periodicity of 4mπ in the Josephson phase which is a tell-tale signature of the existence of parafermion zero modes. We also discuss other signatures such as the dissipative part of the admittance which is accessible to experiment. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N30.00004: Multiferroicity and Topology in Twisted Transition Metal Dichalcogenides Shubhayu Chatterjee, Ahmed Abouelkomsan, Emil J Bergholtz Van der Waals heterostructures have emerged as a highly versatile platform for sharpening our understanding of strong electronic correlations. We study topological flat bands of twisted transition metal dichalcogenides (TMDs) at odd integer fillings via exact diagonalization. We find that Chern insulator phases based on the non-interacting band structure are quite fragile, and give way to spontaneous multiferroic order - coexisting ferroelectricity and ferromagnetism, in presence of long-range Coulomb repulsion. We provide a simple real-space picture to understand the phase diagram as a function of interaction range and strength. Our findings establish twisted TMD homobilayers as a novel and highly tunable platform for multiferroicity, with potential applications to electrical control of magnetism. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N30.00005: Fractionalized holes in one-dimensional Z2 gauge theory coupled to fermion matter --- deconfined dynamics and emergent integrability Aritra Das, Umberto Borla, Sergej Moroz We investigate the interplay of quantum one-dimensional discrete Z2 gauge fields and fermion matter near full filling in terms of deconfined fractionalized hole excitations that constitute mobile domain walls between vacua that spontaneously break translation symmetry. In the limit of strong string tension, we uncover emergent integrable correlated hopping dynamics of holes which is complementary to the constrained XXZ description in terms of bosonic dimers. We analyze numerically quantum dynamics of spreading of an isolated hole together with the associated time evolution of entanglement and provide analytical understanding of its salient features. We also study the model enriched with a short-range interaction and clarify the nature of the resulting ground state at low filling of holes and identify deconfined hole excitations near the hole filling νh = 1/3. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N30.00006: Three-state nematicity and magneto-optical Kerr effect in the charge density waves in AV3Sb5 (A=Cs, Rb, K) Qinwen Deng, Yishuai Xu, Zhuoliang Ni, Yizhou Liu, Brenden Ortiz, Stephen D Wilson, Binghai Yan, Leon Balents, Liang Wu The kagome lattice provides a fascinating playground to study geometrical frustration, topology and strong correlations. The newly discovered kagome metals AV3Sb5 (A = K, Rb or Cs) exhibit phenomena including topological band structure, symmetry-breaking charge-density waves and superconductivity. Nevertheless, the nature of the symmetry breaking in the charge-density wave phase is not yet clear, despite that it is crucial to understand whether the superconductivity is unconventional. In this work, we perform scanning birefringence microscopy on all three members of this family and find that six-fold rotation symmetry is broken at the onset of the charge-density wave transition in all these compounds. We show that the three nematic domains are oriented at 120° to each other and propose that staggered charge-density wave orders with a relative π phase shift between layers is a possibility that can explain these observations. We also perform magneto-optical Kerr effect and circular dichroism measurements and both signals onset at the charge-density wave transition temperature. In addition, we have found that the sign of both signals of CsV3Sb5 can be switched by external magnetic field, indicating broken time-reversal symmetry and the existence of the long-sought loop currents in that phase. |
Wednesday, March 8, 2023 12:42PM - 12:54PM Author not Attending |
N30.00007: Correlated electrons tunnelling trough pseudo Fermi arcs in hyperbolic Fermi surfaces of topological materials Elena Derunova, Mazhar Ali, Angel Rios Ortiz, Jacob Gayles, Yan Sun In the last decades, basic ideas of topology have completely transformed the prediction of quantum transport phenomena. Following this trend, we go deeper into the incorporation of modern mathematics into quantum material science. We rephrase a few major results from algebraic geometry in the language of quantum materials. Particularly, we show that hyperbolic geometry of the Fermi surface results in the Fermi liquid breakdown and correlated transport effects. As a mechanism for realizing these correlations, we introduce pseudo-Fermi arcs connecting separate pockets of hyperbolic Fermi surface. A break of time reversal symmetry via tunneling through a pseud-arc is referred as Fermi Surface Geometry Effect (FS-GE). The predictable power of FS-GE is tested on the spin and anomalous Hall effects, traditionally associated with intrinsic time-reversal symmetry breaking. An index, H_F, quantifying FS-GE in a particular direction, shows a universal correlation (R^2 = 0.97) with the experimentally measured intrinsic anomalous Hall conductivity in that direction, of 16 different compounds spanning a wide variety of crystal, chemical, and electronic structure families, where the topological methods give just R^2 = 0.52. This raises a question about the principal limits of topological physics, dominating now the predictions of non-trivial electron transport, and its transformation into a wider study of bandstructures' and Fermi surfaces' geometries, opening a horizon for prediction of phenomena beyond topological understanding. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N30.00008: Spectra of a Gapped Quantum Spin Liquid with a Strong Chiral Excitation on the Triangular Lattice Thomas Devereaux, Ta Tang, Brian Moritz While a quantum spin liquid (QSL) phase has been identified in the J1-J2 Heisenberg model on a triangular lattice via numerical calculations, debate persists about whether or not such a QSL is gapped or gapless, with contradictory conclusions from different techniques. Moreover, information about excitations and dynamics is crucial for the experimental detection of such a phase. In this work, we use exact diagonalization to characterize signatures of a QSL phase on the triangular lattice through the dynamical spin structure factor S(q, ω) and Raman susceptibility χ(ω). We find that spectra for the QSL phase show distinct features compared to those of neighboring phases; and both the Raman spectra and spin structure factor show gapped behaviour in the QSL phase. Interestingly, there is a prominent excitation mode in the Raman A2 channel, indicating a strong subleading tendency toward a chiral spin liquid phase. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N30.00009: Superconductivity in a topological lattice model with purely-repulsive strong interactions Stefan Divic, Rahul Sahay, Daniel E Parker, Shubhayu Chatterjee, Tomohiro Soejima, Sajant Anand, Johannes Hauschild, Ashvin Vishwanath, Norman Y Yao, Michael P Zaletel We present numerical evidence for superconductivity in a microscopic model with purely-repulsive strong interactions. In particular, we propose and investigate a spinful bilayer system of quarter-flux Hofstadter lattices subjected to opposite magnetic fields, equipped with both local Hubbard interactions and inter-layer tunneling. The underlying band structure possesses nearly flat Chern bands related by time-reversal symmetry and possesses $w_2$ fragile topology, much like the flat bands of magic angle bilayer graphene. At integer filling, strong interactions give rise to flavor-polarized insulating states analogous to quantum Hall ferromagnets. Employing the infinite density matrix renormalization group method on a variety of cylinder circumferences, we find striking numerical evidence for $p$-wave superconductivity upon lightly hole-doping a family of these insulators. We conclude by providing a theoretical understanding of the superconducting instability and outlining a potential experimental implementation in an optical lattice. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N30.00010: Almost ideal Chern bands in periodically strained graphene Qiang Gao, Junkai Dong, Daniel E Parker, Eslam Khalaf We study periodically strained graphene that induces a triangular pseudo-magnetic field (PMF) with zero mean inspired by recent experiments on buckled graphene on NbSe2 substrate. We show that by combining the PMF with a matching periodic scalar field, we can realize an almost ideal isolated narrow band with valley-resolved Chern number C=+-1. By tuning the field, we show that we can achieve an exceptionally small bandwidth that is smaller by at least two orders of magnitude compared to the characteristic energy scale of the system. Furthermore, we show analytically that the band satisfies the ideal band condition up to exponentially small correction which enables us to express their wavefunctions in terms of those of the lowest Landau level in a PMF with a finite average of one flux quantum per unit cell. The combination of narrow bandwidth and ideal band geometry makes the system a perfect platform to achieve strongly correlated topological phases in a setting that is simpler and more tunable compared to conventional graphene-based moire systems. In particular, we show by means of Hartree-Fock numerics that the system realizes a quantum anomalous Hall insulator at odd integer fillings of the flat bands. Upon further fractional filling of the band, we show using exact diagonalization that the system realizes a fractional Chern insulator for parameters in the experimentally feasible range. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N30.00011: Berry curvature induced spontaneous and topological Hall effect in magnetic Weyl semimetallic Nd2Ir2O7 (111) epitaxial thin film MITHUN GHOSH We have performed a temperature and magnetic field dependent magnetotransport study on ~60 nm thick Nd2Ir2O7 (111) epitaxial thin film. Temperature-dependent resistivity shows a semimetallic ground state and observed negligible domain wall conductance in contrast to the bulk sample. Magnetoresistance measurements with the applied magnetic field along (111) direction shows hysteresis, occurs due to plastic deformation of Ir4+ 5d domains distribution via the change in spin structure of Nd3+ 4f moments. Hysteresis in MR vanishes above Nd3+ ordering temperature 15 K, suggests f-d exchange interaction between Ir4+ 5d and Nd3+ 4f moments plays a significant role in Ir4+ domain switching. On the other hand, application of magnetic field along (011) or (001) directions could not modify Ir4+ domain distribution and does not cause any hysteresis in MR. The presence of hysteresis in MR for the applied field along (111) direction and absence for the field along (011) and (001) directions imply subtle interplay between AFM exchange energy and the field-induced Zeeman energy for those particular field directions. In addition to the nontrivial MR phenomena, the measured Hall resistivity (ρxy) shows presence of spontaneous as well as topological Hall components. Observation of large (~75 mΩcm, at 2 K) spontaneous Hall component indirectly confirms presence of Weyl nodes in the electronic band structure of Nd2Ir2O7. A large topological Hall effect also arises due to the noncoplanar spin structure of the Ir4+ moments. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N30.00012: Phase Diagram of Kane-Mele Hubbard model at small doping Gaurav Kumar Gupta, Chin-Sen Ting, Donna Sheng Topological insulators have received a lot of attention in the last decade due to a multitude of prospects, including quantum computing. Kane-Mele (KM) model is one of the first models of a time-reversal invariant topological insulator. Although the topological properties of the KM model have been studied extensively, the effects of interaction are still less explored. In this work, we study the effect of Hubbard interaction at small doping around half-filling. We use the Density matrix renormalization group method to characterize different phases of 6- and 8-leg cylinders. We identify superconducting and spin density wave states at different doping and interaction. Our result shows a rich phase diagram of the Kane-Mele Hubbard model at small doping. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N30.00013: RKKY interactions and Hund's rule in twisted bilayer graphene Haoyu Hu, Alexei Tsvelik, Andrei B Bernevig Twisted bilayer graphene (TBG) has shown two seemingly contradictory characters: (1) quantum-dot-like behavior in STM indicates that then electrons are localized; (2) the transport experiments suggest the itinerant character. Two features can both be captured by a topological heavy-fermion model as demonstrated in Ref. [1]. In this work, based on the Schrieffer-Wolff transformation and the Anderson lattice model defined in Ref. [1], we provide a Kondo-model description of the TBG. In the resulting model, the conduction electrons interact with U(4) local moments via a superexchange and the Hund’s interactions. We calculate the RKKY interactions between U(4) moments induced by these two couplings. By analyzing the behavior of the RKKY interactions, we prove Hund’s rule of the ground state, namely, the wave function tends to be symmetric under permutation of the flavor indices [1]. |
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